Site menuMain pageC3 Project DocsTire Data CalculatorBND
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AlbumsLinksJobs/PartnersContact UsTire Data Calculator(updated
MAR2013)This Tire Data Calculator converts the tire-geometric data
of various RADIAL passenger car tire sizes from theETRTO standard
(European Tire and Rim Technical Organization) into useful data
which can be used insuspension calculations and spreadsheets. It
does not include calculations for commercial or light-truck
tires.Most of the calculations provided here are based upon the
equations found in The Automotive Chassis:Engineering Principles
2nd ed. , Reimpell Stoll Betzler.Your Browser must be able to run
Java to be able to use this program.An explanation for the Input
and Output values can be found below after clicking 'Calculate'.To
calculate the tire-geometric data:Input the following Tire specific
data: Rim Width; Rim Diameter; Tire Aspect Ratio; Tire Section
Width;Select: Tire Load Index Number; Tire Speed Index LetterInput
the following Vehicle specific data: Tire Air Pressure; Vehicle
Speed; Vehicle Corner LoadsLogin formLoginwithuIDOld login formC3
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Tire Data Calculator
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13 19-12-2014 11:00Static Input Data Value Tire 1 Value Tire
2Chosen Rim Width in inches(e.g. 8" as in 8Jx17)Rim Diameter in
inches(e.g. 17" as in 8Jx17)Aspect Ratio in %(e.g. 45% as in 245/45
R 17 95W) **Tire Section Width in mm(e.g. 245 mm as in 245/45 R 17
95W)Tire Load Index Number(e.g. 95 as in 245/45 R 17 95W)Tire Speed
Index letter(e.g. W as in 245/45 R 17 95W)Output Spec. Data Result
Tire 1 Result Tire 2Spec. Design Rim Width(manufacturers measuring
rim)Spec. Tire Outer Diameter(at spec. air pressure and no
load)Spec. Tire Section Width(at spec. air pressure and no
load)Spec. Tire Section Height(at spec. air pressure and no
load)Spec. Static Load Radius(@ spec. maximum load and spec. air
pressure)Spec. Tire Rolling Circumference(@ 60 km/h, spec. load and
spec. air pressure)Spec. Dynamic Rolling Radius(@ 60 km/h, spec.
load and spec. air pressure)Spec. Tire Stiffness Rate(@ spec. load
and air pressure)Tire Air Volume(@ spec. load and air
pressure)Dynamic Input Data Value Tire 1 Value Tire 2Air Pressure
in bar(See the chart below)Vehicle Speed in km/hVehicle Corner Load
in kg(input weights right/left or front/rear)Output Vehicle Data
Result Tire 1 Result Tire 2SearchBND TechSource - Tire Data
Calculator
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13 19-12-2014 11:00Vehicle Tire Section Width(@ vehicle load, speed
and air pressure)Vehicle Tire Section Height(@ vehicle load, speed
and air pressure)Vehicle Tire Deflection(@ vehicle load, speed and
air pressure)Vehicle Tire Rolling Circumference(@ vehicle load,
speed and air pressure)Vehicle Dynamic Rolling Radius(@ vehicle
load, speed and air pressure)Vehicle Tire Stiffness Rate(@ vehicle
load, speed and air pressure)Contact Patch Width(@ vehicle load,
speed and air pressure)Contact Patch Length(@ vehicle load, speed
and air pressure)Contact Patch Area(@ vehicle load, speed and air
pressure)Speedometer Reading(Tire 1 is assumed accurate)Tire
Suspension Comfort ValueLength Conversion CalculatorMillimeters
Inches Centimeters FeetArea Conversion CalculatorSquare Centimeters
Square InchesSpeed Conversion CalculatorKm/h MPHWeight Conversion
CalculatorBND TechSource - Tire Data Calculator
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13 19-12-2014 11:00Pressure Conversion CalculatorBar Kpa PsiRate
Conversion Calculatorkg/mm N/mm lb/inVolume Conversion
CalculatorLiters Cubic InchesBND TechSource - Tire Data Calculator
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13 19-12-2014 11:00Explanation of the Input DataThe chosen rim
width is usually in inches. A rim size of 8Jx17 has a width of 8"
or 203.2 mm.As a rule-of-thumb, you may choose a narrower or wider
rim by inch, but its wise to check with thespecific tire
manufacturer for their approved rim sizes. Choosing a width near
the middle of the approvedrange will give a balance between ride
quality and handling. A wider rim will improve handling at the
expenseof ride quality, while a narrower rim will improve ride
quality at the expense of handling. Consider thesecompromises when
selecting rims.The rim diameter is usually in inches. A rim size of
8Jx17 has a diameter of 17" or 431.8 mm.The aspect ratio or tire
height/width ratio is measured as the section height of tire (SH)
divided by thesection width of tire (SW) and this gives the result
as a percentage. A tire with the size 245/45 R 17 95W hasan Aspect
Ratio of 45%.** If no value is given, for instance as in 165 R 15
S, then the Aspect Ratio is 80%.The tire section width is in mm and
is shown as the first set of numbers on the tire wall, for example;
245mm as on a tire size 245/45 R 17 95W. This is specified in the
ETRTO standards as the width of an inflatedtire mounted on its
design rim, excluding elevations due to labeling, marking,
decorations, or protectivebands or ribs.The tire load index number
is a number shown in the last set of digits on the tire wall, for
example; 95ason a tire size 245/45 R 17 95W. See the tables below
for more information regarding tire loads, speedratings, and air
pressure.The maximum tire load is in kg and can be found on the
chart below based on the tire load index number.The maximum tire
load is used along with the air pressure the corner loads to
calculate the tire rate, which isused to determine the tire
deflection, which is then used for the contact patch calculations.
The conversion oflbs to kg is: (lbs) x 0.453594. The conversion of
kg to lbs is: (kg) x 2.20462.BND TechSource - Tire Data Calculator
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13 19-12-2014 11:00The tire speed symbol is a letter shown in the
last set of digits on the tire wall, for example; W as on a
tiresize 245/45 R 17 95W. See the tables below for more information
regarding tire loads, speed ratings, and airpressure.The vehicle
speed is in km/h and can be changed for tire calculations of speeds
up to 240 km/h. Theconversion of mph to km/h is: (mph) x 1.6093.
The conversion of km/h to mph is: (km/h) x 0.6214.The air pressure
is in bar and can be changed for tire calculations. The air
pressure is vital to safety,durability, comfort, performance and
economy. The air pressure is used along with the loads to calculate
thetire rate, which is used to determine the tire deflection, which
is then used for the contact patch calculations.The conversion of
psi to bar is: (psi) x 0.06895. The conversion of bar to psi is:
(bar) x 14.503775. Note:Since September 2007 all new automobiles
below 10,000 lb (4,500 kg) in weight sold in the United States
arerequired to incorporate a Tire Pressure Monitoring System
(TPMS).The corner loads are in kg and can be changed for tire
calculations. The corner loads are simply the weightin kg under
each tire. These corner loads are used along with the air pressure
and max tire load to calculatethe tire rate, which is used to
determine the tire deflection, which is then used for the contact
patchcalculations. The conversion of lbs to kg is: (lbs) x
0.453594. The conversion of kg to lbs is: (kg) x
2.20462.Explanation of the Output DataThe following details of the
tire sizes are valid according to the ETRTO Standard assuming
proper tire loadrating, speed rating, air pressures, and no wear on
the standard profile. See tables below; courtesy ofContinental
Tire. There are many other factors that affect tire data output
which have not been included inthese calculations. Tire compound
and construction vary from manufacturers. Temperature and
aerodynamicdownforce have also been excluded. These data outputs
assume straight line constant speed, so nolongitudinal or lateral
forces have been included.The spec. design rim width is usually in
inches. The design rim is defined in the ETRTO standards and isused
by the tire manufacturers as a template to measure the tires.The
spec. tire outer diameter (with no load) is based on the input data
and will reflect any deviation inchosen rim width. This can be
measured while the tire/rim assembly is off the car. The spec. tire
outerdiameter shown above will change according to the chosen rim
width.The spec. tire section width (with no load) is the distance
between a tire's sidewalls and measured at thewidest part of the
tire while mounted on the chosen rim. The tire section width varies
approximately 0.2(5mm) for every 0.5 deviation from the design rim
width. This change in width has a direct correlation withthe tire
output data. The spec. tire section width shown above will change
according to the chosen rim width.The spec. tire section height
(with no load) is the radial distance between a tire's rim and the
outsidediameter of the tire while mounted on the chosen rim. The
tire section width varies approximately 0.1(2.5mm) for every 0.5
deviation from the design rim width. This change in height has a
direct correlationwith the tire output data. The spec. tire section
height shown above will change according to the chosen rimwidth.The
spec. static load radius (at maximum load per ETRTO) is the
distance from the center of the wheel tothe road surface when the
car is stationary. This value is calculated under maximum load, at
therecommended tire pressure (see tables below) depending on the
load index and speed rating of each tire. Thestatic radius is used
to calculate the tire stiffness rate. Realistic static radius
values for car tires areapproximately 30 cm. The spec. static
radius shown above will change according to the chosen rim
width.The spec. tire rolling circumference is normally given from
the tire manufacturer. It is the theoreticallength of one rotation
of the tire (circumference) based on the dynamic rolling radius.
The manufacturers testfor tire rolling circumference is calculated
at a speed of 60 km/h (37.3 mph) with an air pressure of 1.8 bar(26
psi) [or 2.3 bar (33 psi) on V-, W-, Y- or ZR tires] and a load
value generally between 30-50% of themaximum load value that was
used to calculate the static radius. This value can be used for
comparison toBND TechSource - Tire Data Calculator
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13 19-12-2014 11:00the tire manufacturer specifications. Realistic
values for car tires are approx 2m. The spec. tire
rollingcircumference shown above will change according to the
chosen rim width.The spec. dynamic rolling radius is normally given
from the tire manufacturer. It is the distance from thecenter of
the wheel to the road surface when the car is moving. The
manufacturers test for dynamic rollingradius is calculated at a
speed of 60 km/h (37.3 mph) with an air pressure of 1.8 bar (26
psi) [or 2.3 bar (33psi) on V-, W-, Y- or ZR tires] and a load
value generally between 30-50% of the maximum load value thatwas
used to calculate the static radius. The spec. dynamic rolling
radius shown above will change according tothe chosen rim width.The
spec. tire stiffness rate is derived from the tire deflection based
on spec. load at spec. air pressurefrom the manufacturer and the
deflection at that spec. It is static therefore the spec. tire
stiffness rate shownabove will only change according to the chosen
rim width.The tire air volume is the volume of air between tire and
rim for a non-loaded tire at spec. air pressure.The vehicle tire
section width (at vehicle load, air pressure and speed) is the
distance between a tire'ssidewalls and measured at the widest part
of the tire while mounted on the chosen rim. This value
iscalculated under vehicle corner load, at the chosen tire air
pressure depending on the load index and speedrating of each tire.
The vehicle tire section width shown above will change according to
the chosen rim width,vehicle corner load, chosen air pressure and
vehicle speed.The vehicle tire section height (at vehicle load, air
pressure and speed) is the radial distance between atire's rim and
the outside diameter of the tire while mounted on the chosen rim.
This value is calculated undervehicle corner load, at the chosen
tire air pressure depending on the load index and speed rating of
each tire.The vehicle tire section height shown above will change
according to the chosen rim width, vehicle cornerload, chosen air
pressure and vehicle speed.The vehicle tire deflection (at vehicle
load, air pressure and speed) is the change in radial distance
fromunloaded tire of the tire at vehicle corner load, air pressure
and speed while mounted on the chosen rim. Thevehicle tire
deflection shown above will change according to the chosen rim
width, vehicle corner load, chosenair pressure and vehicle
speed.The vehicle tire rolling circumference (at vehicle load, air
pressure and speed) is based on the TRC fromthe manufacturer specs,
but includes the inputs of air pressure, corner loads, and vehicle
speed. This value isa function of vehicle speed, tire section width
and height, tire load rating, tire speed rating, and tire
airpressures. Realistic values for car tires are approx 2m. The
vehicle tire rolling circumference shown above willchange according
to the chosen rim width, vehicle corner load, chosen air pressure
and vehicle speed.The vehicle dynamic rolling radius (at vehicle
load, air pressure and speed) is based on the DRR from
themanufacturer specs, but includes the inputs of air pressure,
corner loads, and vehicle speed. This value is afunction of vehicle
speed, tire section width and height, tire load rating, tire speed
rating, and tire airpressures. Realistic values for car tires are
approx 2m. The vehicle dynamic rolling radius shown above
willchange according to the chosen rim width, vehicle corner load,
chosen air pressure and vehicle speed. Forstatic radius at vehicle
corner load and vehicle air pressure input 0 for speed.The vehicle
tire stiffness rate (at vehicle air pressure and speed) is derived
from the tire deflection basedon vehicle static load radius and
dynamic rolling radius from the manufacturer specs. It includes the
inputs ofair pressure and vehicle speed. This value is a function
of vehicle speed, tire section width and height, tireload rating,
tire speed rating, and tire air pressures. The tire stiffness rate
shown above will change accordingto the chosen rim width, chosen
air pressure and vehicle speed. Once established, the tire
stiffness rate WILLchange due to changes in air pressure and
slightly when the vehicle speed changes. Any changes in loadDOES
NOT affect a change in the tire stiffness rate. Think of it like a
spring. The more (or less) load youput on a spring does not change
its rate.The contact patch width is the tread width at the road
surface. This value is a function of vehicle tiresection width, and
aspect ratio. The contact patch width shown above is per ETRTO
specifications. Most of thetire deflection occurs in the sidewalls;
however the contact patch width will change slightly due to air
pressureBND TechSource - Tire Data Calculator
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13 19-12-2014 11:00and corner load changes.The contact patch length
is the tread length at the road surface. The contact patch length
is derived fromthe sidewall deflection. The sidewall deflection is
a function of the tire stiffness rate (which has the airpressure
and speed figured in) and the vehicle corner load. The contact
patch length shown above will changeaccording to the chosen rim
width, vehicle corner load, tire air pressure and the vehicle
speed.The contact patch area (also known as the tire footprint) is
the tread area at the road surface. This is ofcourse the contact
patch width multiplied by the contact patch length. The contact
patch area shown abovewill change according to the chosen rim
width, vehicle corner load, and tire air pressure and the
vehiclespeed.The speedometer reading for alternative tires is
calculated at vehicle speed. Tire 1 is assumed to be at thecorrect
speedometer reading. Tire 2 is compared to Tire 1. The speedometer
deviation should not be morethan +/-8% or +/-8km/h (+/-5 mph) at
100 km/h (62.1 mph) [check your local laws].The tire suspension
comfort value is more important for low cross-section tires (low
AR). These values arefrom 0 (very bad) up to 10 (very good). The
value depends on the vehicle tire stiffness rate, the vehicle
tiresection height, the tire aspect ratio, and tire index ratings.
This dictates the suspension comfort using thebase values gained
from trials with different tires (these values are not the result
of any ETRTO standards).The tire suspension comfort values shown
above are dynamic and will change according to the chosen rimwidth,
the tire aspect ratio, tire index ratings, vehicle corner load,
tire air pressure and the vehicle speed.BND TechSource - Tire Data
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